In a broadband network, if a client sends a network access request, a server which is in the network and is responsible for IP address allocation allocates an IP address to the client sending the network access request, so that the client may access the network. At present, the servers involved in network access of the client in the broadband network are a DHCPv6 server and a DHCPv6 relay server using a standard DHCP protocol. When the client accesses the network, the client sends a DHCP request message to the DHCPv6 relay server, for applying for accessing the network; the DHCPv6 relay server receives and forwards the request message to the DHCPv6 server; after receiving the DHCP request message of the client, the DHCPv6 server records network initialization information including an IP address allocated to the client and its own IP address in a DHCP reply message, and sends the DHCP reply message to the DHCPv6 relay server; and the DHCPv6 relay server forwards the DHCP reply message received from the DHCPv6 server to the client, so that the client obtains the IP addresses, and accesses the network.
In the DHCPv6 protocol, when the client and the DHCPv6 server are not in the same link, a DHCPv6 relay configuration function and a message forwarding function can be implemented on a router, and a DHCPv6 relay agent can effectively solve the problem of address configuration, so as to enable the client to successfully apply for the IP address.
When the client sends the message to the DHCPv6 server, the IP address of the client is not lost in a relayed process; and when the DHCPv6 server returns a message to client, as the relay agent strips a message header of the message sent back from the DHCPv6 server in forwarding the message sent back from the DHCPv6 server, so that the IP address of the DHCPv6 server carried in the message header is discarded. Therefore, the client cannot know the IP address of the DHCPv6 server, so that the client cannot perform source address authentication on the message from the DHCPv6 server, and the client cannot effectively protect the message sent between the DHCPv6 server and the DHCPv6 client.